Accessing member functions of sockaddr_in

Stack Overflow · 01-27-2005, 12:54 PM

Hello,

I am working on a small project in Linux, written in the C language, that allows communication to and from a server. So far I have my concept in mind, and source code close to flawless. Though, I have a small problem. To reduce the size of code used in main, I created a structure to allow the handles of clients, sockets, and other information store in different areas. Though, to make my job easier, I want to pass the address of a sockaddr_in and access its members inside a function.

Though, when I do, it gives an error as the following: "request for member 'sin_family' in something not a structure or union"

Here is a code sample:

Code:

void setInfo(struct sockaddr_in *sock) {
    memset(sock, 0, sizeof(*sock));
    *(sock.sin_family) = AF_INET;
    *(sock.sin_port) = htons(port);
    *(sock.sin_addr.s_addr) = INADDR_ANY;
}

int main() {
    struct sockaddr_in server;

    setInfo(&server);

    return 0;
}

Compiled with GCC 3.4.3 | Slackware 10.0

At this moment, I'm clueless of why it won't accept the indirection (*) operator. Any help would be appreciated.

- Stack Overflow

Matir · 01-27-2005, 01:06 PM

I believe it should be:

Code:

void setInfo(struct sockaddr_in *sock) {
    memset(sock, 0, sizeof(*sock));
    (*sock).sin_family = AF_INET;
    (*sock).sin_port = htons(port);
    (*sock).sin_addr.s_addr = INADDR_ANY;
}

You want to dereference sock, not sock.sin_family... sock.sin_family does not exist.

Alternatively, use struct pointer syntax:

Code:

void setInfo(struct sockaddr_in *sock) {
    memset(sock, 0, sizeof(*sock));
    sock->sin_family = AF_INET;
    sock->sin_port = htons(port);
    sock->sin_addr.s_addr = INADDR_ANY;
}

Stack Overflow · 01-27-2005, 01:16 PM

Thanks Matir,

That did it. I need to be more observant of what I'm dereferencing in the future.

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Matir · 01-27-2005, 03:48 PM

No problem. A couple of questions, out of curiousity:
1. What are you working on, if I can ask?
2. Which of the two methods do you choose to use? I generally use the second just because it looks cleaner, though the first is more explicit.

Stack Overflow · 01-27-2005, 05:11 PM

Hi,

Quote:

1. What are you working on, if I can ask?

I just started learning UNIX Network Programming a few months ago, say, about 2. I have been programming in the C language for a good 4 years. Though, sockets, and other functions are kind of new to me. I occasionally have a problem in my source code, as trivial as this one might I add. To answer this question, I'm just trying to make a test echo server. Though, I am adding a hash table to store and organize all the clients that connect. So I can look them up, remove them, add them, and other fun stuff. It's just to test my C ability.

Quote:

2. Which of the two methods do you choose to use? I generally use the second just because it looks cleaner, though the first is more explicit.

I chose the first, as of now. Since I am passing a few other pointers, for instance integers, I wanted to keep the dereference style the same. Since none of the variables I pass are truely pointers, but rather memory addresses to local variables, I didn't want to get into a habit of using the pointer to struct shorthand (->) in this type of situation. I admit, the second method looks cleaner, though I am looking for more of an explict look.

I've been working on this project for some time now, though now I am developing it under the Linux environment. I've spent a while allowing executable options. And also able to read in a configuration file and parse it. Though, I spent the last few hours cleaning up all the compiler warnings and errors for GCC 3.4.3 since it's a bit more picky than usual, esp. with the -Wall, -pedantic, -ansi, and -std=c89 flags. Though, I managed to make the build perfectly clean. I am considering releasing the source code, but first I need to figure out why all connections never make it through to the server. No matter how many clients I write.

Hope this answers your questions,
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